The present invention relates to novel circulator conductor arrangement. U.S. Pat. No. 6,107,895 describes a circulator in which the conductor arrangement of the present invention may be employed, the disclosure of which is hereby incorporated.
The topology of the conductor arrangement described in U.S. Pat. No. 6,107,895 is shown in FIG. 1. The conductor arrangement is seen to consist of conductors 1, 2 and 3 electrically connected at one end to base 4. Conductors 1, 2 and 3 include pairs of strip conductors 1L,1R;2L,2R and 3L,3R. The conductor arrangement shown in FIG. 1 is for a lumped element circulator. The coupling between strip conductors is largely dependent upon local interactions at strip conductor crossovers. The coupling between strip conductors at crossovers may be qualitatively modelled by considering only the coupling between overlapping portions of the strip conductors (as the fringing fields are incorporated into the model).
FIG. 2 shows an equivalent electrical circuit of the topology shown in FIG. 1 assuming that all coupling is confined between overlapping portions of the strip conductors only. Region 5 shown in FIG. 1 corresponds to the couplings M3R1R and C3R1R shown in the equivalent circuit in FIG. 2. The region 6 indicated in FIG. 1 corresponds to couplings M3R2L and C3R2L. Likewise regions 7 and 8 correspond to couplings M3R1L and C3R1L; and M3R2R and C3R2R shown in FIG. 2. The remaining equivalent values can be easily deduced in a similar manner (i.e. M indicates inductive coupling, C indicates capacitive coupling and 1L, 1R, 2L, 2R and 3L, 3R indicate the crossing strip conductors referred to in FIG. 1).
It will be appreciated that due to the symmetry of the topology shown in FIG. 1 the areas of regions 5, 6, 7 and 8 etc are substantially the same and the angles of crossing strip conductors 1L, 1R, 2L, 2R and 3L, 3R to each other are substantially the same.
In the model described above it has been assumed that the mutual capacitance and inductance between strip conductors is defined only by the coupling between overlapping areas.
It will be appreciated that the mutual capacitance between strip conductors is dependent upon the overlapping area of the strip conductors and the distance between strip conductors. It will also be appreciated that the mutual inductive coupling is dependent upon the angle at which the strip conductors are disposed to one another.
For the arrangement shown in FIG. 1 it will be appreciated that the mutual capacitive and inductive coupling between strip conductors is substantially the same in each region (5, 6, 7, 8 etc) as the overlapping areas and angles of disposition of the crossing strip conductors remain substantially the same.
It would be desirable to alter the mutual inductive and capacitive couplings illustrated in FIG. 2 somewhat independently to assist in optimising phase balance and the amount of coupling between ports. This would improve transmission and impedance matching and isolation between circulator ports.
U.S. Pat. No. 4,246,552 discloses a circulator having v-shaped strip conductors in which pairs of strip conductors converge from the outer edge of the conductor arrangement to join towards the centre thereof. The preferred range of the convergence angle of the pairs of strip conductors is 15-25xc2x0. This means that the strip conductors,of a pair join over a central region of the ferrite, which may adversely affect impedance matching with output ports of the circulator. In this arrangement narrow strip conductors are used and the aim is to increase distributed magnetic coupling between strip conductors. The arrangement is such that 3 conductors cross at conductor crossovers, which prevents substantially independent variation of the coupling between selected pairs of conductors.
It is an object of the present invention to provide circulator conductor arrangements allowing more independent alteration of inductive and capacitive coupling at strip conductor crossovers or to at least provide the public with a useful choice.
According to a first aspect of the invention there is provided a conductor arrangement for a lumped element circulator including a plurality of crossing over strip conductors providing substantially different amounts of coupling between strip conductors at selected individual cross-overs, wherein the local width of one or more strip conductor varies between selected cross-overs to provide different lumped coupling at selected cross-overs and alter the ratio between capacitive and inductive couplings.
According to another aspect of the invention there is provided a conductor arrangement for a lumped element circulator including a plurality of crossing over strip conductors providing substantially different amounts of local coupling between portions of strip conductors at selected cross-overs, wherein the centrelines of each pair of strip conductors are disposed to each other at an angle of less than 10xc2x0.
According to another aspect of the invention there is provided a conductor arrangement for a lumped element circulator including a plurality of crossing over strip conductors providing substantially different amounts of local coupling between strip conductors at selected cross-overs, wherein at least one strip conductor has a transition along its centre line to provide different local lumped coupling at selected cross-overs.
According to a further aspect of the invention there is provided a conductor arrangement for a lumped element circulator including a plurality of crossing over strip conductors providing substantially different amounts of coupling between strip conductors at selected cross-overs, wherein the centre lines of the strip conductors follow curvilinear paths and the arrangement is such as to provide different local lumped coupling at selected cross-overs.
Preferably each conductor comprises a pair of strip conductors. The strip conductors are preferably arranged in an overlying spaced apart crossing arrangement.
According to one aspect of the invention the width of one or more strip conductor varies along the length of the strip conductor. The width of a strip conductor may taper from one end of the strip conductor to the other. Preferably all conductors taper in the same manner. Preferably the angle of taper is less than 10xc2x0 from the centre line of the conductor to an outside edge of a conductor, more preferably the angle of taper is less than 5xc2x0 and more preferably less than 2xc2x0.
The variation of width of strip conductors is preferably identical for each pair of strip conductors.
According to another aspect of the invention the centre lines of each pair of strip conductors are non-parallel. The centre lines of pairs of strip conductors may converge. Preferably the angle of convergence of the centre lines is less than 20xc2x0, more preferably less than 10xc2x0, more preferably less than 6xc2x0. Alternatively, there may be transitions between portions of strip conductors. Alternatively the centre lines of pairs of strip conductors may follow curvilinear paths.
According to another aspect, tabs may be provided at regions where a strip conductor overlaps with one or more other strip conductor, or notches may be provided in a strip conductor where the strip conductor overlaps with other strip conductors.
According to a further aspect the distance between strip conductors may vary for different crossings of strip conductors.